Ex-ATCO input.
Airfield search radars do not need to operate at long range: 60 or so will suffice.
Military and Civil Area control radars used to work out to much longer ranges - up to 120/150 in my day.
Air Defence radars work to even longer (classified) ranges.
Those are primary radar ranges ... SSR coverage will be similar.
As noted (and illustrated in a link) previously, Malaysian coastal (Air Defence?) radars reached almost to the Vietnam coastline at the FLs we are looking at.